1. Field of the Invention
The present invention relates to a high-frequency heat-bonding method for layers of material used to finish automotive vehicle interiors, including seat cushions. The invention relates more specifically to a method of heat-bonding foam resin material to outer finishing layers without using adhesives or chemical heat-bonding agents. Even more specifically, there is disclosed a method for selecting a urethane foam most suitable for use in the method of the present invention.
2. Description of the Prior Art
In order to finish automotive vehicle interiors, generally, an interior finishing material such as nylon cloth, a cushioning material such as foamed urethane, and a lining material such as nylon cloth, cotton cloth (calico), or non-woven material are piled up in order and heat-bonded to each other at the desired positions. In some cases, however, only a finishing material and foamed resin material are heat-bonded, omitting the lining material.
Conventionally, in the case where the interior finishing material, a foamed resin material and a lining material are heat-bonded together at the necessary positions, a high-frequency welder has been used to heat these three materials.
In the prior-art heat bonding method, however, since the melting temperature of the foamed resin material is higher than that of the interior finishing material, it is difficult to melt only the foamed material without melting the interior finishing material. Further, when these two materials are heat-bonded without melting the finishing material, it is difficult to heat-bond the layers firmly.
To overcome this problem, it has been necessary to apply an appropriate heat-bonding agent or adhesive agent, in advance, onto one or both sides of the foamed resin material locally, or to impregnate a powder heat-bonding agent thereinto or liquid adhesive agent thereon for bonding the layers of these materials together.
In practice, during the above-mentioned method where a heat-bonding agent or an adhesive agent is applied to the foamed resin cushion before heating, it is difficult to apply or impregnate the heat-bonding agent or the adhesive agent correctly to the desired positions. In addition, the extra manufacturing processes involved results in an increase in manufacturing cost.